[c-nsp] ADSL and "Capacity Used"

[Lukas Tribus]

Hi,


> Been googling for a bit now, but this information is seemingly missing my
> browser. I know that it's not really important, but for my own curiosity
> and sanity. What "Capacity" does "Capacity Used" refer to on a ADSL WIC when
> issuing the show atm int xxx command?

Capacity is the downstream/upstream rate your telephone line can theoretically
achieve, from the point of view and calculations of the modem firmware (based
on attenuation and noise, for example).

However most of the times, the central-office modem (the DSLAM) will decide
about the ADSL rate. So if you bought 640k downstream from your provider
and the telephone line is short and with very low attenuation, the capacity
will probably be about 20megs, while your provider will limit your downstream
ADSL rate to 640k (not speaking about policing IP traffic here, but your modem
will train at 640k). The "Capacity Used" percentage will therefor be low.

Similar, if the DSLAM is configured in RAM (rate adaptive mode), the DSLAM
decides based on his own target SNR margin (and other metrics), so 100%
"capacity used" is rare to achieve.



Regards,

Lukas